1. Field of the Invention
The present invention concerns an intersomatic cage adapted to be inserted from the posterior approach between the vertebral bodies of two vertebrae, in particular lumbar vertebrae, and ancillary equipment for installing the cage. A cage of this kind is used to fuse the vertebral bodies after surgical removal of the disc, preserving the intervertebral distance.
2. Description of the Prior Art
A prior art intersomatic lumbar cage has a hollow cylindrical body provided with a hemispherical anterior end and closed by a posterior screw plug. Elongate openings or slots are formed in the cylindrical body and/or the cylindrical body has a knurled roughened peripheral surface for facilitating bone ingrowth. The body may be prefilled with bone graft material, called as "allograft", and the plug is screwed and locked to the body. At least one such cage is inserted between two vertebral bodies using appropriate ancillary equipment. Cages of this type are described in International Patent Applications Nos. WO89/12431 and WO92/14423 and European Patent Application No. 0,307,241.
The installed cage has top and bottom bearing surfaces in contact with the vertebral bodies. These bearing surfaces are narrow portions of the cylindrical surface of the cage body. The dimensions of the cage are usually selected from a range of a few sizes to suit the anatomy of the patient. Once chosen, the cage has fixed dimensions, however. It is usually desirable during surgery to adjust the relative position of the two vertebrae which are to be "joined" by fusing their vertebral bodies via the graft material, in particular their angular position in the anterior-posterior plane, which is known as the lordosis angle. Adjustment during surgery of this kind is not possible with an intersomatic cage of the above prior art type.